<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 200px;
            height: 200px;
            background-color: purple;
        }
    </style>
</head>

<body>
    <div></div>
    <script>
        var div = document.querySelector("div");
        window.addEventListener("resize", function() {
            if (window.innerWidth < 800) {
                div.style.display = "none";
            } else {
                div.style.display = "block";
            }
        })
    </script>
</body>

</html>